Does the soda industry manipulate research on sugary drinks' health effects?

New research raises questions about the credibility of medical studies on obesity that are funded by the beverage industry. (Prakash Singh / AFP-Getty Images)

One hundred percent.

That is the probability that a published study that finds no link between sugar-sweetened beverage consumption and poorer metabolic health was underwritten by the makers of sugar-sweetened beverages, or authored by researchers with financial ties to that industry.

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Compare that figure with 2.9%. Among published studies that found that sugary beverage consumption is linked to higher rates of obesity and diabetes, fewer than 3% were underwritten by the sugar-sweetened beverage industry or authored by researchers who receive money from them.

That stark mismatch is revealed in an analysis of the last 15 years' worth of experimental research studies that explored the health effects of sugary soda consumption. The review, published Monday in the Annals of Internal Medicine, was conducted by a team of researchers at UC San Francisco.

The group's findings led them to an equally stark conclusion:

"This industry," they wrote, referring to companies that market sugar-sweetened beverages, "seems to be manipulating contemporary scientific processes to create controversy and advance their business interests at the expense of the public's health."

This industry seems to be manipulating contemporary scientific processes to ... advance their business interests at the expense of the public's health.

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The controversy over the health effects of sugary drink consumption appears to be very real: Of the 60 experimental studies included in the new analysis, 26 articles — 43% failed to uncover any link between sweetened soda drinking and either obesity or metabolic dysfunction. While the remaining 34 articles — about 57% — did find higher rates of those health problems and consumption of sugary drinks, the scientific evidence would suggest it's a toss-up.

But to suggest that scientific conclusions cannot be influenced by financial interests would be wrong, say the authors. Nudged by a sponsor, or simply mindful of a financial supporter's concerns, a researcher with financial ties to an industry affected by his or her research could make many subtle decisions about data that can skew outcomes.

"It's way too simple to say that companies buy the results they want," New York University food researcher Marion Nestle said Monday. But, she added, "there is something about funding that leads — almost certainly unconsciously and unwittingly — to skewing studies to get the desired results.This is not hard to do."

She says it has been shown in studies in which pharmaceutical companies fund clinical trials of drugs they make.

The take-home message, says Nestle: "If you read research that favors surprising food products, ask who funded it." If industry-funded, it needs "even more skepticism than is usual."

Worldwide, beverage companies sell between $200 billion and $800 billion worth of products a year, about 65% of which is sweetened with sugar or high-fructose corn syrup, Nestle reports in her book "Soda Politics: Taking on Big Soda (and Winning)." Both directly and through their industry group, the American Beverage Assn., beverage giants such as Coca-Cola, PepsiCo, Dr Pepper Snapple give financial support to researchers and nutritionists across the United States.

They have a substantial stake in the outcome of research that explores the relationship between a worldwide run-up in obesity and diabetes and increases in consumption of their products.

In a statement issued Monday, the American Beverage Assn. said "we too want a strong, healthy America," adding, "we have a right – and a responsibility – to engage in scientific research."

"The research we fund adheres to the highest standards of integrity for scientific inquiry based on recognized standards by prominent research institutions," the association said. "It contributes to the body of scientific knowledge, meets the needs of regulatory agencies and enables consumers to make informed decisions."

The new analysis appears to be the first ever to rigorously explore the relationship between beverage industry financial ties and the findings of clinical research on sugar-sweetened soda consumption.

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To gauge the effect of industry ties on research findings, the group considered 60 experimental studies that set out to explore whether the consumption of sugary drinks increased the incidence of obesity or metabolic dysfunction, including type-2 diabetes. They ruled out studies that were funded by commercial competitors that do not produce sugar-sweetened beverages (such as companies that bottle water only).

Led by Dr. Dean Schillinger, the UC San Francisco group considered only studies that explored the link between drink consumption and metabolic problems experimentally — by comparing the outcomes of participants who did not consume sugar-sweetened beverages with those who did.

In some of those 60 studies, comparison groups would have been created by researchers who assigned subjects randomly to one "experimental condition" or another. In other studies included in the analysis, researchers took advantage of existing databases that allowed the comparison of people who chose to consume sugar-sweetened beverages with those who did not.

Just over half of the studies considered in the newly published analysis were "meta-analyses" of such experimental studies. Essentially, such studies aggregate the findings of many experiments to reach a conclusion.

These studies are thought to have strengths as well as weaknesses. Because they rely on many smaller studies conducted under widely different circumstances, meta-analyses are often discounted by researchers. At the same time, meta-analyses that show strong convergence on a given finding can help distill scientific consensus, precisely because they demonstrate that studies conducted differently have reached similar conclusions.

In a letter published Monday, Schillinger and his team caution that industry sponsorship of research and of researchers is likely influencing the dietary advice that Americans get along a wide front. In laying the scientific foundation for the drafting of U.S. "Dietary Guidelines" every five years, the U.S. Department of Agriculture does not specifically consider industry funding of research as a source of bias, they write.

In its statement Monday, the ABA noted that Dr. Schillinger, the study's lead author, is a paid expert in a lawsuit brought against San Francisco by the beverage industry in July. Citing infringement of the industry's 1st Amendment rights, that lawsuit seeks to prevent implementation of a new San Francisco ordnance that would require health warnings on ads for sugar-sweetened beverages that appear on buses, billboards and city property.

"It's ironic that he would write about bias in research when he himself is clearly not an impartial researcher," the ABA said. "This paper is the latest in a trend of pro-tax forces writing speculative opinion papers to influence voters a week before a vote on several ballot initiatives to tax beverages."